Arugula in Zone 7A — Pacific Northwest

Arugula, with its distinctive peppery bite, is a fantastic addition to any Pacific Northwest garden. It’s incredibly versatile – perfect in salads, on pizzas, or as a zesty pesto – and thrives in our mild summers and cool nights, which actually enhance its flavor. Plus, the satisfaction of harvesting fresh greens from your backyard, especially when they're as easy to grow as arugula, is hard to beat.

While we might struggle a bit with heat-loving plants during our short summers, arugula is right at home here. Our 183-day growing season gives you plenty of time to sow multiple crops, ensuring a steady supply of this tasty green from spring through fall. Timing is key, but with a little planning, you'll be enjoying homegrown arugula in no time.

Starting arugula indoors isn't essential in our climate, but it can give you a head start, especially if you're eager to get the first harvest as early as possible. If you want to go this route, sow seeds indoors from early to late March, about three weeks before you plan to transplant them outside.

Use seed trays filled with a good seed-starting mix and keep them in a warm location, ideally around 70°F. A heat mat can help with germination, especially with our overcast spring days. Provide ample light; a grow light is beneficial, as natural light can be limited. Remember to water from the bottom to prevent damping off.

Transplant your arugula seedlings outdoors from early April through mid May, once they have a few sets of true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Choose a spot with full sun to partial shade and space the plants about 6 inches apart. Our wet springs mean you'll want to ensure good drainage to prevent root rot. Keep an eye on the forecast, as a late frost can still happen, and be prepared to cover your seedlings if necessary.

Direct sowing arugula is the easiest and most common method for PNW gardeners. You can sow seeds directly into the garden from late March through late August, ensuring a continuous harvest throughout the growing season. Arugula is fast-growing, so you can sow new seeds every few weeks.

Prepare the soil by loosening it and removing any rocks or debris. Arugula prefers soil that is at least 50°F for optimal germination. Sow seeds about ¼ inch deep and 6 inches apart. Keep the soil consistently moist, and you should see seedlings emerge within a week. The only downside is that it bolts in heat, so plant accordingly.

Arugula needs consistent moisture to thrive, especially during our dry summer months. Aim to keep the soil evenly moist but not waterlogged. The finger test is a great way to check: stick your finger about 2 inches into the soil; if it feels dry, it's time to water.

During the spring and fall, when we get more rainfall, you might only need to water once or twice a week, providing about 1 inch of water each time. In the drier summer months, increase watering to every other day or daily, depending on the weather. Watering at the base of the plant is preferable to overhead watering, as it reduces the risk of fungal diseases and keeps the leaves dry.

Signs of underwatering include wilting leaves and slow growth, while overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, can help retain moisture in the soil and keep the roots cool during the warmer months.

You can expect your first arugula harvest about 40 days after planting, which means you can start harvesting as early as early May if you planted in early spring. The best time to harvest is when the leaves are young and tender, about 2-3 inches long, for a milder flavor. Larger leaves will have a more pronounced peppery taste.

To harvest, simply snip off the outer leaves with scissors or a knife, leaving the inner leaves to continue growing. This cut-and-come-again method allows for continuous production throughout the season. To extend your harvest into the fall, consider planting a final crop in late August through late September. As the first frost approaches in mid- October, you can cover your plants with a row cover or cold frame to protect them from the cold and extend the growing season.

Arugula, like any plant, can have its challenges, even here in the PNW. Here are the most common problems you might encounter:

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves, especially on young seedlings. You might also see small, dark beetles jumping when disturbed.
• What causes it: Flea beetles are small jumping beetles that feed on leaves. They are most damaging to small, young plants.
• How to fix/prevent it: Row covers are your best defense to protect seedlings during their vulnerable stage. You can also delay planting until plants are larger and more resilient. Kaolin clay coating can deter them, and neem oil spray can help control infestations. Interplanting with basil or catnip can also help repel them.

Bolting in Heat

• What it looks like: The plant sends up a flower stalk, and the leaves become tough and bitter. Harvest quality declines rapidly.
• What causes it: Arugula is a cool-season crop and bolts when temperatures rise. Extended warm temperatures above 80°F will trigger bolting.
• How to fix/prevent it: Time your plantings for cool weather in spring and fall. Choose bolt-resistant varieties if possible. Provide shade during warm spells with shade cloth. Mulch to keep the soil cool. Harvest frequently to encourage leaf production before bolting progresses.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: A strong water spray can knock them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap can be used for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer, as it attracts them.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides. Leaves brown and die from the bottom up.
• What causes it: Downy mildew is an oomycete pathogen that spreads in cool, humid conditions via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants properly. Water at the base, never overhead. Copper-based fungicides can be used for prevention. Plant resistant varieties where available.

Pacific Northwest Specific Challenges: While late blight isn't a direct threat to arugula, our cool, wet springs can create favorable conditions for downy mildew. Our short summers mean that you need to be mindful of bolting and time your plantings accordingly. Slugs can also be an issue, especially for young seedlings, so use slug bait or other control methods if necessary.

Arugula benefits from companion planting. Lettuce and spinach make good companions because they share similar growing requirements and won't compete for resources. Carrots and beets are also beneficial, as they help loosen the soil, which improves drainage. Onions can help deter pests like aphids. Avoid planting arugula near strawberries, as they can attract pests that also affect arugula.